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This is one of the most common problems we get asked, and it's also the one we are least equipped to answer, but you are most equipped to answer yourself.
Let me just explain what the error means: You have tried to use a variable, property, or a method return value but it contains null - which means that there is no instance of a class in the variable.
It's a bit like a pocket: you have a pocket in your shirt, which you use to hold a pen. If you reach into the pocket and find there isn't a pen there, you can't sign your name on a piece of paper - and you will get very funny looks if you try! The empty pocket is giving you a null value (no pen here!) so you can't do anything that you would normally do once you retrieved your pen. Why is it empty? That's the question - it may be that you forgot to pick up your pen when you left the house this morning, or possibly you left the pen in the pocket of yesterdays shirt when you took it off last night.
We can't tell, because we weren't there, and even more importantly, we can't even see your shirt, much less what is in the pocket!
Back to computers, and you have done the same thing, somehow - and we can't see all your code, much less run it and find out what contains null when it shouldn't.
But you can - and Visual Studio will help you here. Run your program in the debugger and when it fails, VS will show you the line it found the problem on. You can then start looking at the various parts of it to see what value is null and start looking back through your code to find out why. So put a breakpoint at the beginning of the method containing the error line, and run your program from the start again. This time, VS will stop before the error, and let you examine what is going on by stepping through the code looking at your values.
But we can't do that - we don't have your code, we don't know how to use it if we did have it, we don't have your data. So try it - and see how much information you can find out!
Bad command or file name. Bad, bad command! Sit! Stay! Staaaay...
I'm creating a C# app with an SQL Server database.
In one module, the user has the option to filter the results by clicking on one of the two radio buttons (one is already selected by default), and I don't want to have to keep on re-accessing the database each time the user switches between the filters as it might consume time when the app has to load the data.
I'm using DataAdapter, DataTable, and DataGridView
Is there a way for me to somehow store the data from the database in a cache and then access them and show results that match the filter? How?
Hi, i try to change the background color of RadGridView in background color property but it is not work!! please help me.
Note: I don't want change the background color of row or cell, i want change the background color of RadGridView white to other color? plese help me...
I have been looking for a way to detect when the a console application has ended. I want the ability to do some cleanup. Similar to Application.ApplicationExit in forms applications. I've scoured google, code project, msdn, etc. but no solid solution.
I thought about simply launching a cleanup thread at the start of the program and have it Join the main thread. Once that happens perform cleanup. I tried a test application (see code below):
staticvoid Main(string args)
Thread cleanupThread = new Thread(cleanupThreadStart);
privatestaticvoid cleanupThreadStart(object state)
Thread mainThread = (Thread)state;
Console.WriteLine("cleanupThreadStart: Waiting for main thread to exit.");
Oddly, this solution works from within VS when I start with debugging (F5), meaning that the main thread will end and the cleanup thread will complete the join and I'll see the console printout. However if I start without debugging (ctrl+F5 or simply run the executable directly) the program hangs because the main thread ends but the cleanup thread never completes the Join. I've tried attaching to the process from within VS during the hang and I can see that the main thread is no longer present but the cleanup thread is still waiting for the Join to complete.
Does anybody know why this works with debugging active but not without it? Does anybody have any other clever way of detecting that the application is about to end (similar to Application.ApplicationExit)?
For now I've got a workaround to just create my own "main" thread which executes the normal application code. Then my cleanup thread joins with this thread before cleanup. This seems to work fine.
When the debugger is attached, it will keep the main-thread alive, since you're debugging. Without the debugger, the main-thread is halted. The application will close as soon as all foreground threads close.
There is no event that says that a console-application is about to be aborted with Ctrl-C. The mainthread is simply terminated; hence it will not execute any events.
Bastard Programmer from Hell
If you can't read my code, try converting it here[^]